812 Fuel Gage

i have opened my fuel sender in tank unit. I posted pictures of what it looks like before and after. Did the oil level sender too. That unit is slightly different and it was filled with horrible sludge.


Gary Parsons

That info was just what I needed for my 810! I also had the same reading for full on the gauge no matter what the fuel level was. Turns out my gauge was mis-wired but I didn't understand how it worked with the 2 opposing electro-magnets with one needing full 6v from ground and the other getting power from the sender to counter the other electro-magnet and therefore indicate the fuel level. Once I had that it wasn't too terrible to figure out which wire went to which post as well as making sure the meter was properly grounded.

Perfect explanation of a fixed problem. If my gauge has the same issue I can relate to this and know how to fix it.


Gary Parsons

Yes, I figured it out but the issue was VERY hard to find. Turns out it was a bad ground inside the gage itself. It is a balanced magnet type. One magnet pulls the gage needle to full and the other pulls the gage needle to zero. The one that pulls to zero uses full 6 volt current. The one that pulls toward full uses 6 volt diminished by the resistor in the sender. The circuit for the magnet that pulls toward zero has a path to ground that relies on a copper strip hitting against the gage case. Mine did NOT so the only magnet that worked was the one toward full. I corrected it by reorienting the gage within the housing to assure that the copper strip hit the housing. Now it works!

Have you figured out what the electrical issue was yet? Please, When you find it post it here so many others like myself may benefit from the issue and repair.


Gary Parsons

The system did work correctly for more than 10 years - this is a change.

I took the senders out for bench test so the wires in the car are not a cause. I connected the gage and the senders in a bench test with no car wiring. Thanks for helping.

With either or both senders disconnected, the gage reads zero as it should with no ground at all. With either connected to the gage (even one at a time) and with either manually rotated to their "empty" positions, the gage reads full as if there is a short through the senders. However, there is no short through either sender - they have matching and what seem like correct resistances - about 130 at empty and near zero at full. Further, there is no short at the push button selector switch. The gage seems to go to full with even very low voltage.

When you state "both positions".. Are you saying both the oil level and the gas tank level show full no matter what levels are really in there? If so you might disconnect the oil level sender and then the gas tank sender to see if either of them are causing this issue. My guess is the oil level sender in the oil pan has failed but testing will tell for sure. Both my gas tank and oil pan sender are apart on my bench if you need pictures of the internals.


Gary Parsons

There are NO shorts to ground in the gage itself - sorry for the confusion in the original message.

My fuel/oil gage goes to "full" on both positions despite reality. There are no shorts, both senders have realistic resistances (about 120 ohm empty, abut 0 full) and all wires are intact. There are shorts to ground in the gage and its coils are intact. I can't figure it out. Help.